In some cases (e.g., hash-based classes) iteration over an entry set requires
the creation of a large number of Map.Entry objects. Some
fastutil maps might return entry set
objects of type FastEntrySet: in this case, fastIterator() will return an iterator that is guaranteed not to create a
large number of objects, possibly by returning always the same entry
(of course, mutated), and fastForEach(Consumer) will apply the
provided consumer to all elements of the entry set, which might be
represented always by the same entry (of course, mutated).